Method for reducing ash content of polypropylene and application of pyrrolidine ionic liquid

Abstract

The invention provides a method for reducing ash content of polypropylene and application of pyrrolidine ionic liquid. The invention provides a method for reducing ash content of polypropylene, which comprises the following steps: A) mixing, stirring, washing and filtering pyrrolidine ionic liquid with a structure as shown in a formula (I), a washing solution and polypropylene powder to obtain reacted polypropylene powder; b) mixing and flushing the reacted polypropylene powder and flushing fluid, filtering and drying to obtain the low-ash-content polypropylene, according to the invention, the pyrrolidine ionic liquid with a standard chemical structure is used as the deliming agent of the polypropylene, and the pyrrolidine ionic liquid can interact with metal ash in the polypropylene to a certain extent, so that the ash content in a product obtained after washing the polypropylene is sharply reduced. Experimental results show that after the polypropylene powder with the ash content of 25-600ppm is subjected to ash removal treatment by adopting the method provided by the invention, the ash content of the product can be lower than 10ppm.

Description

Technical Field

[0001] The invention relates to the technical field of polyolefins, in particular to a method for reducing ash content of polypropylene and application of pyrrolidine ionic liquid. Background Art

[0002] In recent years, polypropylene, as an important synthetic resin material, has been widely used in many fields such as plastic products, textiles, and chemicals. With the continuous upgrading of downstream industry technology and the expansion of application areas, the national polypropylene market has a growing demand for ultra-low ash polypropylene. According to data from market research institutions, it is expected that by 2025, the global polypropylene market will reach US$270 billion, and low and ultra-low ash polypropylene materials will become a major trend in the market.

[0003] The ash content of polypropylene mainly comes from impurities in raw materials and residual impurities in the main catalyst, co-catalyst, electron donor and other materials used in the polymerization process. At present, there are two main production processes for ultra-low ash polypropylene. One is to use special catalysts, which requires high catalyst research and development capabilities of enterprises. The other is to change the washing method. This process is relatively easy, but it is difficult to produce products with extremely low ash content.

[0004] Therefore, it is very necessary to provide a method for reducing the ash content of polypropylene. Summary of the invention

[0005] In view of this, the technical problem to be solved by the present invention is to provide a method for reducing the ash content of polypropylene. The method of the present invention has a high removal rate of polypropylene ash.

[0006] The present invention provides a method for reducing the ash content of polypropylene, comprising the following steps:

[0007] A) mixing a pyrrolidine ionic liquid of formula (I), a washing liquid and a polypropylene powder, stirring, washing and filtering to obtain a reacted polypropylene powder;

[0008] B) mixing the reacted polypropylene powder and the washing liquid, washing, filtering, and drying to obtain low-ash polypropylene;

[0009]

[0010] Wherein, R1 is selected from one or more of C2-C10 alkyl and allyl groups; preferably, R1 is one or more of ethyl, propyl, butyl, pentyl, hexyl, octyl, decyl and allyl groups.

[0011] R2 is selected from one or more of bromide ion, chloride ion, iodide ion, nitrate ion, bis(fluorosulfonyl)imide ion, dinitrile amide ion, trifluoromethanesulfonate ion, acetate ion, tetrafluoroborate ion and hexafluorophosphate ion;

[0012] R3 is methyl or H.

[0013] In some preferred embodiments of the present invention, the pyrrolidine ionic liquid of formula (I) is specifically the following structure:

[0014]

[0015]

[0016]

[0017]

[0018]

[0019]

[0020]

[0021] The present invention does not limit the source of the pyrrolidine ionic liquid of the above formula (I), which may be commercially available or synthesized according to the method disclosed in the prior art.

[0022] The present invention uses the pyrrolidine ionic liquid of the above structure as a deashing agent for polypropylene powder. The pyrrolidine ionic liquid can interact with the metal ash in the polypropylene to a certain extent, so that the ash content in the product after the polypropylene powder is washed is sharply reduced. Experimental results show that after the polypropylene powder with an ash content of 25-600ppm is deashed by the method provided by the present invention, the ash content of the product can be less than 10ppm.

[0023] The present invention first mixes the pyrrolidine ionic liquid of formula (I), washing liquid and polypropylene powder. The present invention does not limit the specific method of the above mixing, which is well known to those skilled in the art. Then, the mixture is stirred, washed and filtered to obtain the reacted polypropylene powder.

[0024] The present invention has clearly described the pyrrolidine ionic liquid of formula (I) above, which will not be repeated here.

[0025] The ash content of the polypropylene powder of the present invention is preferably 25-600ppm, specifically 25ppm, 30ppm, 50ppm, 80ppm, 100ppm, 110ppm, 130ppm, 150ppm, 200ppm, 220ppm, 250ppm, 300ppm, 330ppm, 360ppm, 400ppm, 450ppm, 480ppm, 500ppm, 550ppm or 600ppm; or a range between any two of the above.

[0026] In some specific embodiments, the volume ratio of the pyrrolidine ionic liquid to the washing liquid is 1:(1-20); specifically, it can be 1:1, 1:2, 1:3, 1:4, 1:5, 1:6, 1:7, 1:8, 1:9, 1:10, 1:11, 1:12, 1:13, 1:14, 1:15, 1:16, 1:17, 1:18, 1:19, 1:20. Or a range between any two of the above.

[0027] In the method provided by the present invention, the washing method is preferably washing with an organic solvent. Among them, the organic solvent used for the organic solvent washing is preferably one or more of alkane organic solvents, alcohol organic solvents, ketone organic solvents, ester organic solvents, dichloromethane, and chloroform. The alkane organic solvent is one or more of n-butane, n-pentane, isopentane, n-hexane, n-heptane, n-decane, and n-dodecane; the alcohol organic solvent is one or more of methanol, ethanol, propanol, isopropanol, butanol, and hexanol; the ketone organic solvent is one or more of acetone, butanone, 2-pentanone, 3-pentanone, and acetylacetone; the ester organic solvent is one or more of methyl formate, ethyl acetate, methyl propionate, isopropyl acetate, isobutyl formate, and dimethyl carbonate.

[0028] According to the present invention, the mass ratio of the pyrrolidine ionic liquid to the polypropylene powder is (0.5-10):1. Specifically, it can be 0.5:1, 1:1, 1.5:1, 2:1, 3:1, 4:1, 5:1, 6:1, 7:1, 8:1, 9:1, 10:1. Or a range between any two of the above.

[0029] In the present invention, the washing temperature is preferably 25-105°C, specifically 25°C, 30°C, 35°C, 40°C, 45°C, 50°C, 55°C, 60°C, 65°C, 70°C, 75°C, 80°C, 85°C, 90°C, 95°C, 100°C, 105°C; or a range between any two of the above.

[0030] The washing time is preferably 0.5 to 6 hours, specifically 0.5 hours, 1 hour, 1.5 hours, 2 hours, 2.5 hours, 3 hours, 3.5 hours, 4 hours, 4.5 hours, 5 hours, 5.5 hours or 6 hours, or a range between any two of the above.

[0031] After washing, the washing liquid is preferably removed by suction filtration.

[0032] The reacted polypropylene powder and the washing liquid are mixed, washed, filtered and dried to obtain low-ash polypropylene.

[0033] The flushing liquid of the present invention comprises one or more of an alkane organic solvent, an alcohol organic solvent, dichloromethane or chloroform; the hydrocarbon organic solvent is one or more of n-butane, n-pentane, isopentane, n-hexane, n-heptane, n-decane and n-dodecane; the alcohol organic solvent is one or more of methanol, ethanol, propanol, isopropanol, butanol and hexanol.

[0034] According to the present invention, the mass ratio of the flushing liquid to the reacted polypropylene powder is (0.5-20):1; specifically, it can be 0.5:1, 1:1, 1.5:1, 2:1, 3:1, 4:1, 5:1, 6:1, 7:1, 8:1, 9:1, 10:1, 11:1, 12:1, 13:1, 14:1, 15:1, 16:1, 17:1, 18:1, 19:1, 20:1; or a range value between any two of the above.

[0035] The temperature of the flushing of the present invention is -10 to 35°C;

[0036] The flushing and filtering times of the flushing liquid of the present invention are 2 to 4 times, specifically 2 times, 3 times, and 4 times, and each time is flushing first and then filtering; the single washing time is 0.5 to 3 hours, specifically 0.5 hours, 1 hour, 1.5 hours, 2 hours, 2.5 hours, and 3 hours.

[0037] The present invention does not limit the specific filtering method, which can be well known to those skilled in the art.

[0038] In some specific embodiments, the drying temperature is 40-105° C., specifically 40° C., 45° C., 50° C., 55° C., 60° C., 65° C., 70° C., 75° C., 80° C., 85° C., 90° C., 95° C., 100° C., 105° C., or any range between any two of the above.

[0039] The present invention provides a low-ash polypropylene obtained by processing by the method described in any one of the above technical solutions.

[0040] The present invention also provides the use of a pyrrolidine ionic liquid of formula (I) as a polypropylene ash removal agent;

[0041]

[0042] Among them, R1 is selected from one or more of C2-C10 alkyl and allyl groups; R2 is selected from one or more of bromide ion, chloride ion, iodide ion, nitrate ion, bis(fluorosulfonyl)imide ion, dinitrile amide ion, trifluoromethanesulfonate ion, acetate ion, tetrafluoroborate ion and hexafluorophosphate ion; R3 is methyl or H.

[0043] That is, the present invention provides the use of the pyrrolidine ionic liquid with the structure of formula (I) in reducing the ash content of polypropylene.

[0044] The above-mentioned pyrrolidine ionic liquid has a good effect as a polypropylene ash removal agent; in the method provided by the present invention, the polypropylene product preferably has an ash content of less than 10 ppm; the content of magnesium, aluminum and titanium in the low-ash polypropylene is preferably 0.01 to 2.5 ppm.

[0045] In the method provided by the present invention, the low-ash polypropylene product finally obtained can be dried and ashed, and then the contents of different elements therein can be determined using an inductively coupled plasma spectrometer.

[0046] The method provided by the present invention uses a pyrrolidine ionic liquid with a standard chemical structure as a deashing agent for polypropylene powder. The pyrrolidine ionic liquid can interact with the metal ash in the polypropylene to a certain extent, so that the ash content in the product after the polypropylene powder is washed is sharply reduced. More specifically, the method provided by the present invention has the following technical advantages:

[0047] Good safety performance: Ionic liquids have low vapor pressure, are non-flammable, have good stability, and low toxicity, which greatly reduces the unsafe factors for people and objects during the deashing process of polypropylene.

[0048] Wide range of applications: This deashing method has low requirements on raw materials and can remove ash from different raw materials under a variety of conditions.

[0049] High deashing efficiency: The pyrrolidine ionic liquid is "designable". Adding a solvent to dissolve the ionic liquid reduces its usage while enabling full contact with the raw materials, resulting in excellent deashing efficiency.

[0050] The production cost is controllable: the ionic liquid used in the deashing process and the organic reagent used in the washing process can be recovered, purified and recycled, which reduces the production cost.

[0051] The present invention provides a method for reducing the ash content of polypropylene and the application of pyrrolidine ionic liquid. The present invention provides a method for reducing the ash content of polypropylene, comprising the following steps: A) mixing the pyrrolidine ionic liquid of the structure of formula (I), a washing liquid and a polypropylene powder, stirring, washing and filtering to obtain a polypropylene powder after reaction; B) mixing the polypropylene powder after reaction and a washing liquid, washing, filtering and drying to obtain a low-ash polypropylene; the present invention uses a pyrrolidine ionic liquid of a standard chemical structure as a deashing agent for polypropylene, and the pyrrolidine ionic liquid can interact with the metal ash in the polypropylene to a certain extent, so that the ash content of the product after the polypropylene is washed is sharply reduced. Experimental results show that after the polypropylene powder with an ash content of 25-600ppm is deashed by the method provided by the present invention, the ash content of the product can be lower than 10ppm. DETAILED DESCRIPTION

[0052] The present invention provides a method for reducing the ash content of polypropylene and the application of pyrrolidine ionic liquids. Those skilled in the art can refer to the content of this article and appropriately improve the process parameters to achieve it. It should be particularly pointed out that all similar replacements and modifications are obvious to those skilled in the art, and they all fall within the scope of protection of the present invention. The method and application of the present invention have been described through preferred embodiments, and relevant personnel can obviously modify or appropriately change and combine the method and application of this article without departing from the content, spirit and scope of the present invention to implement and apply the technology of the present invention.

[0053] It should be understood that the expression "one or more of..." includes each of the items recited after the expression individually and in various different combinations of two or more of the recited items, unless otherwise understood from the context and usage. The expression "and / or" in combination with three or more recited items should be understood to have the same meaning, unless otherwise understood from the context.

[0054] The use of the terms "comprising", "having" or "containing", including their grammatical synonyms, should generally be understood as open and non-restrictive, for example not excluding other unrecited elements or steps, unless otherwise specifically stated or otherwise understood from the context.

[0055] In this application, the term "and / or" describes the association relationship of associated objects, indicating that there may be three relationships. For example, A and / or B can represent: A exists alone, A and B exist at the same time, and B exists alone. A and B can be singular or plural.

[0056] It should be understood that the order of steps or the order in which certain actions are performed is not important as long as the present invention remains operable. In addition, two or more steps or actions may be performed simultaneously.

[0057] The use of any and all examples or exemplary language, such as "for example" or "including", herein is intended only to better illustrate the invention and does not limit the scope of the invention unless otherwise claimed. No language in this specification should be construed as indicating that any non-claimed element is essential to the practice of the invention.

[0058] In addition, the numerical ranges and parameters used to define the present invention are approximate values, and the relevant values ​​in the specific embodiments have been presented as accurately as possible. However, any numerical value inherently inevitably contains standard deviations due to individual test methods. Therefore, unless otherwise expressly stated, it should be understood that all ranges, quantities, values ​​and percentages used in this disclosure are modified by "about". Here, "about" generally means that the actual value is within plus or minus 10%, 5%, 1% or 0.5% of a specific value or range.

[0059] It should be understood that in the various embodiments of the present application, the size of the serial numbers of the above-mentioned processes does not mean the order of execution, some or all of the steps can be executed in parallel or sequentially, and the execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of the present application.

[0060] Some cases are recorded in the embodiments and comparative examples of the present invention, wherein the embodiments show certain implementation modes of the present invention. However, this does not mean that the effects of the present invention can only be achieved in these cases.

[0061] In order to further illustrate the present invention, a method for reducing ash content of polypropylene and application of pyrrolidine ionic liquid provided by the present invention are described in detail below in conjunction with examples.

[0062] Example 1

[0063] N-propyl-N-methylpyrrolidine chloride is used to remove ash from polypropylene, and its structural formula is:

[0064]

[0065] The specific ash removal process is as follows: first, N-propyl-N-methylpyrrolidine chloride (200 g) is dissolved in ethanol (500 ml) and mixed evenly, the mixed solution is stirred and reacted with polypropylene powder (80 g, ash content is 200 ppm) at 90°C for 2 hours, and then the washing liquid is removed by suction filtration; next, the obtained polypropylene powder is added to dichloromethane (200 g), washed at 25°C for 0.5 hours and then filtered, the dichloromethane rinsing and filtration are repeated twice, and finally dried at 70°C to obtain a low-ash polypropylene product.

[0066] Example 2

[0067] N-butyl-N-methylpyrrolidine bromide is used to remove ash from polypropylene, and its structural formula is:

[0068]

[0069] The specific ash removal process is as follows: first, N-butyl-N-methylpyrrolidine bromide (220g) is dissolved in a mixture of n-hexane and acetylacetone (800ml in total) and mixed evenly, the mixture is stirred and reacted with polypropylene powder (110g, ash content is 350ppm) at 105°C for 4h, and then the washing liquid is removed by suction filtration; next, the obtained polypropylene powder is added to dichloromethane (300g), washed at 35°C for 1h and then filtered, the dichloromethane rinsing and filtration are repeated twice, and finally dried at 90°C to obtain a low-ash polypropylene product.

[0070] Example 3

[0071] N-butyl-N-methylpyrrolidine bis(fluorosulfonyl)imide salt is used to remove ash from polypropylene, and its structural formula is:

[0072]

[0073] The specific ash removal process is as follows: first, N-butyl-N-methylpyrrolidine bis(fluorosulfonyl)imide salt (130 g) is dissolved in n-heptane (450 ml) and mixed evenly, and the mixed solution is stirred with polypropylene powder (160 g, ash content is 500 ppm) at 25°C for 3 hours, and then the washing liquid is removed by suction filtration; next, the obtained polypropylene powder is added to a mixture of dichloromethane and ethanol (a total of 180 g), washed at 25°C for 1.5 hours and then filtered, and the dichloromethane and ethanol mixture are rinsed and filtered three times, and finally dried at 40°C to obtain a low-ash polypropylene product.

[0074] Example 4

[0075] N-propyl-N-methylpyrrolidone iodide is used to remove ash from polypropylene, and its structural formula is:

[0076]

[0077] The specific ash removal process is as follows: first, N-propyl-N-methylpyrrolidinodium iodide (100 g) is evenly mixed in dichloromethane (200 g), and the mixed solution is stirred and reacted with polypropylene powder (100 g, ash content is 130 ppm) at 90°C for 2 hours, and then the washing liquid is removed by suction filtration; next, the obtained polypropylene powder is added to n-hexane (200 g in total), washed at 25°C for 0.5h and then filtered, and the n-hexane rinsing and filtration are repeated twice, and finally dried at 75°C to obtain a low-ash polypropylene product.

[0078] Example 5

[0079] N-butyl-N-methylpyrrolidine dinitrile amine salt is used to remove ash from polypropylene, and its structural formula is:

[0080]

[0081] First, N-butyl-N-methylpyrrolidine dinitrile amine salt (90 g) was dissolved in n-hexane (500 ml) and mixed evenly. The mixed solution was stirred with polypropylene powder (90 g, ash content was 90 ppm) at 50° C. for 2.5 h, and then the washing liquid was removed by suction filtration; next, the obtained polypropylene powder was added to dichloromethane (100 g), washed at 25° C. for 1 h and then filtered, and the dichloromethane rinsing and filtration were repeated twice. Finally, it was dried at 45° C. to obtain a low-ash polypropylene product.

[0082] Example 6

[0083] N-butyl-N-methylpyrrolidine hexafluorophosphate is used to remove ash from polypropylene, and its structural formula is:

[0084]

[0085] The specific ash removal process is as follows: first, N-butyl-N-methylpyrrolidine hexafluorophosphate (110 g) is dissolved in n-hexane (150 ml) and mixed evenly, and the mixed solution is stirred with polypropylene powder (100 g, ash content is 50 ppm) at 25°C for 4 hours, and then the washing liquid is removed by suction filtration; next, the obtained polypropylene powder is added to a mixture of dichloromethane and ethanol (a total of 100 g), washed at 25°C for 1 hour and then filtered, and the dichloromethane and ethanol mixture are rinsed and filtered twice, and finally dried at 40°C to obtain a low-ash polypropylene product.

[0086] Comparative Example 1

[0087] The difference from Example 1 is that no N-propyl-N-methylpyrrolidino chloride salt is added.

[0088] The specific ash removal process is as follows: first, ethanol (500 ml) and polypropylene powder (80 g, ash content of 200 ppm) are stirred and reacted at 90°C for 2 hours, and then the washing liquid is removed by suction filtration; next, the obtained polypropylene powder is added to dichloromethane (200 g), washed at 25°C for 0.5 hours and then filtered, the dichloromethane rinsing and filtration are repeated twice, and finally dried at 70°C to obtain a low-ash polypropylene product.

[0089] Comparative Example 2

[0090] The difference from Example 1 is that there is no heating and stirring.

[0091] N-propyl-N-methylpyrrolidine chloride is used to remove ash from polypropylene, and its structural formula is:

[0092]

[0093] The specific ash removal process is as follows: first, N-propyl-N-methylpyrrolidine chloride (200 g) is dissolved in ethanol (500 ml) and mixed evenly, the mixed solution is reacted with polypropylene powder (80 g, ash content is 200 ppm) for 2 hours, and then the washing liquid is removed by suction filtration; next, the obtained polypropylene powder is added to dichloromethane (200 g), washed at 25°C for 0.5h and then filtered, the dichloromethane rinsing and filtration are repeated twice, and finally dried at 70°C to obtain a low-ash polypropylene product.

[0094] Comparative Example 3

[0095] The difference from Example 1 is that there is no dichloromethane filtering and rinsing step.

[0096] N-propyl-N-methylpyrrolidine chloride is used to remove ash from polypropylene, and its structural formula is:

[0097]

[0098] The specific ash removal process is as follows: first, N-propyl-N-methylpyrrolidine chloride (200 g) is dissolved in ethanol (500 ml) and mixed evenly, the mixed solution is stirred and reacted with polypropylene powder (80 g, ash content is 200 ppm) at 90°C for 2 hours, and then the washing liquid is removed by suction filtration; finally, it is dried at 70°C to obtain a low-ash polypropylene product.

[0099] Comparative Example 4

[0100] The difference from Example 4 is that the ionic liquid is triethyloxonium tetrafluoroborate.

[0101] Triethyloxonium tetrafluoroborate is used to remove ash from polypropylene, and its structural formula is:

[0102]

[0103] The specific ash removal process is as follows: first, triethyloxonium tetrafluoroborate (100 g) is evenly mixed in dichloromethane (200 g), and the mixed solution is stirred and reacted with polypropylene powder (100 g, ash content is 130 ppm) at 90°C for 2 hours, and then the washing liquid is removed by suction filtration; next, the obtained polypropylene powder is added to n-hexane (200 g in total), washed at 25°C for 0.5h and then filtered, and the n-hexane rinsing and filtration are repeated twice, and finally dried at 75°C to obtain a low-ash polypropylene product.

[0104] Comparative Example 5

[0105] The difference from Example 4 is that the ionic liquid is N-ethyl-N-methylpiperidinium chloride.

[0106] N-ethyl-N-methylpiperidinium chloride is used to remove ash from polypropylene, and its structural formula is:

[0107]

[0108] The specific ash removal process is as follows: first, N-ethyl-N-methylpiperidinium chloride (100 g) is evenly mixed in dichloromethane (200 g), the mixed solution is stirred and reacted with polypropylene powder (100 g, ash content is 130 ppm) at 90°C for 2 hours, and then the washing liquid is removed by suction filtration; next, the obtained polypropylene powder is added to n-hexane (200 g in total), washed at 25°C for 0.5h and then filtered, the n-hexane rinsing and filtration are repeated twice, and finally dried at 75°C to obtain a low-ash polypropylene product.

[0109] Effect evaluation

[0110] The ash content and metal element content of the polypropylene products obtained in Examples 1 to 6 and Comparative Examples 1 to 3 were measured, and the test results are as follows:

[0111]

[0112] The data in the above table show that the pyrrolidine ionic liquid used in the present invention has an excellent deashing effect on polypropylene powder containing a relatively high ash content.

[0113] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A method for reducing the ash content of polypropylene, characterized in that: The steps include: A) mixing a pyrrolidine ionic liquid of formula (I), a washing liquid and a polypropylene powder, stirring, washing and filtering to obtain a reacted polypropylene powder; B) mixing the reacted polypropylene powder and the washing liquid, washing, filtering, and drying to obtain low-ash polypropylene; Among them, R1 is selected from one or more of C2-C10 alkyl and allyl groups; R2 is selected from one or more of bromide ion, chloride ion, iodide ion, nitrate ion, bis(fluorosulfonyl)imide ion, dinitrile amide ion, trifluoromethanesulfonate ion, acetate ion, tetrafluoroborate ion and hexafluorophosphate ion; R3 is methyl or H.

2. The method according to claim 1, characterized in that The R1 is one or more of ethyl, propyl, butyl, pentyl, hexyl, octyl, decyl, and allyl.

3. The method according to claim 1, characterized in that The pyrrolidine ionic liquid of formula (I) has the following structure:

4. The method according to claim 1, characterized in that: The volume ratio of the pyrrolidine ionic liquid to the washing liquid is 1:(1-20); the mass ratio of the pyrrolidine ionic liquid to the polypropylene powder is (0.5-10):

1.

5. The method according to claim 1, characterized in that The washing liquid is one or more of an alkane organic solvent, an alcohol organic solvent, a ketone organic solvent, an ester organic solvent, dichloromethane or chloroform; The alkane organic solvent is one or more of n-butane, n-pentane, isopentane, n-hexane, n-heptane, n-decane and n-dodecane; the alcohol organic solvent is one or more of methanol, ethanol, propanol, isopropanol, butanol and hexanol; the ketone organic solvent is one or more of acetone, butanone and 2-pentanone, 3-pentanone and acetylacetone; the ester organic solvent is one or more of methyl formate, ethyl acetate, methyl propionate, isopropyl acetate, isobutyl formate and dimethyl carbonate.

6. The method according to claim 1, characterized in that The flushing liquid includes one or more of an alkane organic solvent, an alcohol organic solvent, dichloromethane or chloroform; The hydrocarbon organic solvent is one or more of n-butane, n-pentane, isopentane, n-hexane, n-heptane, n-decane and n-dodecane; the alcohol organic solvent is one or more of methanol, ethanol, propanol, isopropanol, butanol and hexanol.

7. The method according to claim 1, characterized in that The washing temperature of step A) is 25-105°C; the washing time is 0.5-6h.

8. The method according to claim 1, characterized in that Step B) the mass ratio of the flushing liquid to the reacted polypropylene powder is (0.5-20):1; The temperature of the flushing is -10 to 35°C; the number of flushing is 2 to 4 times; the time of a single flushing is 0.5 to 3 hours; The drying temperature is 40-105°C.

9. A low-ash polypropylene, characterized in that: The method is obtained by processing according to any one of claims 1 to 8.

10. Application of pyrrolidine ionic liquid of formula (I) as a polypropylene ash removal agent; in, R1 is selected from one or more of C2-C10 alkyl and allyl groups; R2 is selected from one or more of bromide ion, chloride ion, iodide ion, nitrate ion, bis(fluorosulfonyl)imide ion, dinitrile amide ion, trifluoromethanesulfonate ion, acetate ion, tetrafluoroborate ion and hexafluorophosphate ion; R3 is methyl or H.

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